Welding is a process for joining materials (such as metals and thermoplastics) together through fusion. For example, to weld two metals together, a heat source may be applied to melt the base metals and fuse them together. A filler material may also be added to the joint between the two metals to strengthen the connection. Various types of welding processes, systems, and machines to join materials together are generally known. For example, two well-known, traditional welding processes are oxy-fuel welding (“OFW”), wherein a mix of fuel gasses and oxygen is used to produce the weld, and gas tungsten arc welding (“GTAW”), wherein a non-consumable tungsten electrode is used to produce the weld.
Some welding processes, known as welding overlays or cladding, may be used to apply metal to the surface of an object rather than to join two objects together. One such process is “hardfacing,” wherein material is deposited onto a metallic surface or substrate of an object to change the properties of the object. For example, a harder or more resilient coating material can be applied to the surface of an object made from a weaker or less resilient base material to increase the strength or resilience of the object. Hardfacing may be done either to increase an object's wear resistance or to restore the surface of an object that has been worn down.
One example of a welding process used for hardfacing is plasma transferred arc (“PTA”) welding. PTA welding is a versatile method which may be used to deposit high-quality metallurgically fused deposits on relatively low cost metallic surfaces. Soft alloys, medium and high hardness materials, and carbide composites can be deposited on a variety of substrates in order to achieve diverse properties including improved mechanical strength, wear and corrosion resistance, and decreased creep deformation (which is also referred to as “cold flow”). As a result, PTA welding has several significant advantages over traditional welding processes such as OFW and GTAW. PTA welding generally utilizes a lower heat input than traditional welding processes, allowing a thinner layer of deposit material to be used. Further, PTA welding can utilize powdered deposit material. This makes PTA welding significantly less expensive and more versatile than many traditional welding processes.
However, performing hardfacing using a process such as PTA welding (or even more traditional welding processes) requires that an operator possesses a significant amount of experience, skill, and judgment in order to perform the welding processes consistently and effectively. Hardfacing is most commonly done by hand; the operator must manually apply the filler material using a hand-held welding device. This requires that an operator possesses a significant level of skill, as the surface of the substrate constantly changes during the welding process and is generally uneven. As a result, performing hardfacing welding operations by hand often produces welds of variable width and thickness, potentially compromising the integrity of the weld over the lifespan of the part.
Occasionally, machines are used to perform a hardface welding process. Applying a weld overlay to a workpiece using a machine, as is necessary in performing a hardfacing welding process, requires an intimate understanding of the three-dimensional position and movement of the torch and the workpiece relative to one another. During the welding process, the heat source or torch must precisely move across the surface of the device and apply the correct amount of heat and filler material at every point. For a flat surface, the torch moves both laterally and longitudinally across the surface.
For a more complicated surface (such as a curved surface), this process is complicated further in that the part or substrate to which the welding process is being applied will generally need to be moved during the welding process in order to provide access to the entire surface to be hardfaced. This necessitates that the operator understand, and be able to accurately describe to the machine, the motion of the torch with reference to the moving workpiece. For example, for a cylindrical part, such as the workpiece or part 100 shown in FIG. 1, a hardface weld 106 may be applied circumferentially around a portion of the surface 102 of the part 100. Rather than moving the torch (not shown) around the workpiece 100, which requires complicated machinery, the workpiece 100 may be rotated while the torch only moves in the lateral direction x. The motion of the torch therefor must be described based on the rotation of the workpiece 100; the rotation of the workpiece 100 moves the torch in the longitudinal direction y along the surface 102 of the workpiece 100. Thus, in determining how to apply the weld overlay, the operator must not only calculate how to apply the overlay in three dimensions, but also account for the rotation of the workpiece 100 during the application of the overlay.
While various types of machines and devices have been created to assist with welding processes (such as computer numerical control or “CNC” welding devices), significant input and guidance is still required from the operator, creating the potential for significant error and raising the cost of the welding process. For example, to apply hardfacing to a cylindrical part, such as workpiece 100, using a known CNC welding device, the operator must define a variety of movement parameters in the CNC welding device's programming menu so that the CNC welding device will move the torch and part 100 in the desired manner. For a flat surface, these parameters include (i) the distance the torch moves in the lateral direction x (the oscillation width, or w); (ii) the speed at which the torch moves in the lateral direction x (the oscillation speed, or Vo); (iii) the speed at which the torch moves in the longitudinal direction y (the welding speed, or Vs); and (iv) the distance the torch moves in the longitudinal direction y for each oscillation (the pitch, or p). For a workpiece 100 with a curved surface, the operator must instead define the speed at which the workpiece 100 rotates (the rotational speed, or u). The operator will frequently need to calculate the rotational speed in dimensions that are difficult to visualize or understand, such as “degrees per minute” (“°/min”), based on the desired pitch and welding speed.
In order to obtain a precise hardfacing process, these settings must be calculated and entered correctly, which requires the operator to spend significant time double or triple-checking his or her work. Further, these settings are strongly depending on the particular geometry of a given workpiece. This requires the operator to accurately measure each individual workpiece and input new settings for each workpiece, or for each portion of a workpiece's surface with a different geometry. For example, separate sets of calculations are necessary for the first portion 102 and the second portion 104 of the workpiece 100 in FIG. 1, as the first and second portions have different diameters. Similarly, new calculations are required if the oscillation width is different for a particular portion of the welding process. If two or more variations occur between workpieces, it can be extremely difficult or impossible for an operator to adjust the new parameters so as to apply a consistent weld overlay between the workpieces, resulting in potentially significant variations in the hardfacing welds for the different workpieces. This is particularly problematic in manufacturing environments with tight tolerances.
Further, existing systems and methods of welding provide no opportunity for standardization of the welding process, resulting in a high failure risk, and require a highly educated welding operator. Such systems and methods provide less flexibility and greater complexity, as a variety of different welding procedure specifications (“WPSs”) are required to account for the various types of physical geometries and welding characteristics that the welding operator will encounter.
Accordingly, there has been identified a need for an improved system and method for automated or machine-assisted welding that overcomes the limitations, shortcomings and disadvantages of known systems and methods.